1. Field of Invention
This present invention relates to a preparation method of one contact material, more particularly to a method of preparing Ag-based oxide contact materials with directionally arranged reinforcing particles.
2. Description of Related Arts
Electrical contacts, one of the core components of electrical switches, are in charge of the connection and disconnection of electrical circuits and load current. The electrical contact materials are widely applied to the manufacture of both low and high voltage electrical apparatus including various air switches, relays and ac/dc contactors and covering a wide range of fields such as civil use, industry, military, aerospace, aviation and information. In recent years, with the development of the high voltage transmission and transformation grid towards large capacity and extra high voltage (EHV), there has been a high demand for the improvement of automatic level and sensitivity of the low voltage distribution system and control system and modernization of the electronic industrial products. As a result, there seems to be an increasingly high requirement on electrical contact material for more functions and longer service life. Therefore, researches on new Ag-based composites and preparation methods have been continuously carried out. Metallic oxide (MeO) particles reinforced Ag-based composite has been widely studied and applied due to its good thermal conductivity, electrical conductivity, resistance to welding and resistance to electrical wear. Meanwhile, as the preparation of metallic oxide (MeO) particle reinforced Ag-based composite could be achieved at a low cost and in a relatively simple preparation process such as the traditional metal working process, the development of the material seems to have a promising future.
Research results on the particle-reinforced Ag-based electrical contact materials are stated as below:
1) Chinese patent: preparation method of carbon-coated nickel nano-particle reinforced Ag-based composite, application number: 200810153154.9, publication number: CN101403105A.
2) Chinese patent: preparation method of metal matrix composite, application number: 200410064970.4, publication number: CN1760399A.
3) Chinese patent: preparation method of particle-reinforced metal matrix composite, application number: 200810018200.4, publication number: CN101285187A.
4) Chinese patent: preparation method of nano rare earth mixed with AgSnO2 electrical contact alloy by chemical co-precipitation method, application number: 200410073547.0, publication number: CN100481289C.
At present, the preparation methods of particle-reinforced Ag-based electrical contact materials can be classified into three categories. First is the conventional powder metallurgy sintering method, whose process includes powder mixing→isostatic pressing→sintering→hot pressing→extruding, and secondary processing such as rolling or forging. During powder mixing of this method, the reinforced particles prone to clustering cannot be dispersively distributed thereby undermining the performance of the product. Second is to pre-process the reinforcing particles [literature 1], reinforcing particle-matrix [literature 2], or matrix [literature 3] based on the conventional method. Third is to prepare well distributed composite powder by chemical co-precipitation method [literature 4], and then process it with cold pressing, sintering, re-pressing and extruding. Despite that the second and third method can dispersedly distribute the reinforcing particles into the Ag matrix, study has shown that when the reinforcing particles (oxide) are small (nanoscale), the dispersed distribution can increase the contact area between the reinforcing particles and Ag matrix. Therefore, the electron scattering effect is greatly reinforced and electrical resistance of the contact materials can be greatly increased, which shall greatly affect the performance of the product. Meanwhile, the dispersively distributed small reinforcing particles (oxide) can improve the intensity and hardness of the material, and can improve resistance to mechanical wear of the material. However, it can also greatly decrease the elongation of the materials resulting in poor ductility and difficulty in processing.